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Asked: 2026-05-26T18:22:12+00:00

I am trying to understand when a developer needs to define a C variable

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I am trying to understand when a developer needs to define a C variable with preceding ‘_’. What is the reason for it?

For example:

uint32_t __xyz_ = 0;
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  1. Editorial Team

    Maybe this helps, from C99, 7.1.3 (“Reserved Identifiers”):

    • All identifiers that begin with an underscore and either an uppercase letter or another
      underscore are always reserved for any use.

    • All identifiers that begin with an underscore are always reserved for use as identifiers
      with file scope in both the ordinary and tag name spaces.

    Moral: For ordinary user code, it’s probably best not to start identifiers with an underscore.

    (On a related note, I think you should also stay clear from naming types with a trailing _t, which is reserved for standard types.)

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